1. Field of the Invention
The present invention relates to systems and methods of designing, operating and maintaining satellite communication systems and in particular to a system and method for mitigating communications interference between satellite communications systems in different orbits.
2. Description of the Related Art
The need for worldwide communications communication is growing rapidly. This growth is propelled by the convergence of the telecommunications and computer industries, the rapid expansion of wireless technologies and the ever-expanding use of the Internet, which has made significant inroads into everyday life. The growth of small offices and home offices, the emergence of a mobile work force, and the development of multimedia applications have also contributed to the rapid growth of data related communications.
The emerging market for Internet/Intranet/Extranet connections requires a satellite system capable of providing short-delay, global-coverage, and high-bandwidth communication. The rapidly growing demand for Internet connections which require broadband data communication, known as access services (AS).
Internet service providers (ISPs) and related telecommunications providers are currently enhancing existing technologies and creating new infrastructures to support Internet services. Web access, electronic commerce, and remote access will soon be services available to everyone. Online data applications are rapidly going beyond basic email and file transfer functionality to encompass services such as videoconferencing, interactive multimedia collaborations and multicasting.
As Internet and multimedia applications increasingly drive the rapid growth of internetworking service markets, end-users of these services require that service providers transmit and process more data more rapidly.
Online user growth is skyrocketing as users discover the World Wide Web as a superior technology platform for delivering news, information, correspondence and entertainment. By the year 2000, the number of Internet users is expected to reach close to 300 million worldwide with more than four million business sites established on the Internet. Over 580 million computers in use by the year 2000, and total global IP services revenues are forecast to top $16 billion by 2002. Further, total online U.S. households are forecasted to reach 35 million by the year 2000.
Also fueling the demand for more bandwidth is e-commerce, which is growing at a remarkable rate. Increasingly, businesses realize that creating a business presence on the Internet allows them to reach more people economically. Consumers have embraced e-commerce due to its convenience and timesaving nature. As a result, e-commerce is expected to grow to $400 billion by the year 2002, accounting for approximately 8% of all retail purchases worldwide.
These millions of online transactions will require immediate connectivity solutions, especially in areas of the world where little or no Internet infrastructure is available creating a comprehensive terrestrial infrastructure will be too costly and time consuming. Moreover, intelligent agents that can facilitate user tasks (such as price comparisons) will further increase bandwidth needs.
Another development fueling the demand for bandwidth is Internet telephony service, a nascent market poised for dramatic growth. It has been forecasted that by 1999, Internet phone service worldwide will grow from virtually nothing to a $560 million business and, by 2001, packet-switched networks will account for about one percent of global long distance trafficxe2x80x94about 12.5 billion minutes worth.
From the foregoing, it can be seen that there is a need for a system providing high bandwidth data communication services. This need can be met with conventional terrestrial data communication systems; however, such systems are difficult and expensive to implement. The need can also be met with satellite systems in geosynchronous or geostationary (GSO) orbits, but the number of orbital slots is limited, and it is difficult devise earth stations of a reasonable power level and complexity that can communicate with such satellites.
There is therefore a need for a non-geostationary system NGSO provides high bandwidth communications. At the same time, communications with the NGSO system must not interfere with existing or future GSO systems. The present invention satisfies that need with a system constellation that meets a significant part of the enormous demand for bandwidth for global network interconnectivity.
To address the requirements described above, the present invention discloses a satellite communications system architecture providing high bandwidth service to a variety of widely-dispersed customers.
One aspect of the present invention is described in a satellite system deployed in a LEO, MEO, or combined LEO/MEO constellation, using narrow communication antenna beamwidths and intelligent handovers to mitigate interference with other satellites deployed in space. The satellite system provides a wide variety of two-way, broadband services to both business and residential customers.
The satellite system includes a plurality of satellites, for example, a constellation of seventy satellites and preferably includes radio communication links, intersatellite links, and telemetry, tracking, and command (TTandC) links. Through the use of spot beam and dual polarization technologies, each satellite can reuse the communication spectrum up to 30 times.
The present invention also uses spectrum sharing to avoid causing harmful interference with spacecraft in geostationary or geosynchronous (collectively referred to hereinafter as GSO) orbits. The satellite system provides broadband communications services to a wide range of users both in the United States and throughout the world and can efficiently use the Ku-band and enhance the capabilities of existing GSO satellite systems. The satellite system meets the needs of the emerging market of Internet/Intranet/Extranet connection by providing short delay, global coverage, and high bandwidth communication through a spectrum sharing-oriented system design, simple payload architecture, and small user terminals.
The satellite system meets a broad range of communications needs through services at various data rates, including data rates that range from 512 KBPS up to 10 MBPS. The satellite system further provides fast network connections for interactive broadband services to a wide range of customers, especially the personal or the small-office-home-office (SOHO) users. The satellite system implements an Internet-access service to serve the rapidly growing demand for Internet connections. An Intranet-access service also provides broadband connections from remote business sites to the center of a corporate wide area network (WAN). Finally, the present invention also provides an Extranet access service to extend the Intranet connection to remote locations for multi-national corporations especially for those business site in remote/rural areas and in developing countries.
The satellite system constellation design provides global coverage while fully protecting GSO satellite systems from unwanted interference. The system design allows resources to be focused on high demand areas, such as the continental United States (CONUS) and Europe, while providing significant service to lower-demand areas.
With its global coverage over under-served parts of the globe, the present system enables people everywhere access to the advantages of e-commerce. The satellite system""s low latency will facilitate access to interactive Internet protocol (IP) communication and voice services.
The satellite communication system can provide communications capabilities that advances the National Information Infrastructure (NII) and Global Information Infrastructure (GII) by increasing the amount and variety of high-data-rate broadband interactive services throughout the world; multi-rate, multi-functional telecommunications services in general and high speed data access to the Internet in particular. The design of the system ensures that this capability can be provided at low cost with a short deployment time.
This is especially important due to a large increase in data traffic created by Internet use, which has highlighted the need for the deployment of alternative paths for data traffic. The present invention provides a data infrastructure that complements and interfaces with existing networks to support a wide range of communications services.
With its high data rate telecommunications capability, the present invention supports commercial communications including high-speed information transfers and interactive multimedia exchanges between businesses and customers, thereby creating new efficiencies and productivity for businesses that need to be connected to international networks. The present invention also allows developing countries will be able to use capacity of the communications satellite system to improve their own national telecommunications infrastructures without incurring the high cost and suffering the delay of installing towers, laying cable, and building terrestrial network facilities in all areas.
The present invention also enables users to readily update and retrieve applications, create secure IP-multicast sessions, and conduct high-speed file transfers; support media streaming; participate in interactive distance learning; and perform database updates and replication to and from personal computers (PCs). The satellite communications system provides Internet access to personal and small/home office users (SOHO) and Intranet/Extranet access to all businesses. It also enables related services such as IP telephony and e-commerce.
The satellite system design supports efficient, cost-effective provision of services. This is accomplished in part by the use of a spot beam technology that increases the efficiency with which spectrum is reused. This allows the present invention to provide more capacity for populated areas of the world. The characteristics of the system are ideal for supporting highly interactive broadband services. The present system will help build a broadband access infrastructure to meet all these requirements for ready access to more bandwidth.
The satellite communications system is designed to serve the global broadband market by providing interactive services to the mass market and applications such as high-speed Internet access, IP telephony and e-commerce.
In accordance with the foregoing, the invention is also described by a method for defining the communications satellite system. The method comprises the steps of identifying a plurality of communication interference scenarios; categorizing an interference requirement specifying a maximum interfering signal strength statistic at each of the second satellites according to a frequency of occurrence; identifying at least one interference mitigation strategy for each scenario and each category of interference requirement; determining the effectiveness of each identified interference mitigation strategy in mitigating interference for each of the scenarios and categories of interference requirement; and selecting at least one of the identified mitigation means for the first satellite communication system according to the determined effectiveness of the interference mitigation strategy.
Yet another aspect of the invention is described by a method for mitigating communication interference between a first satellite communicating with a first ground station and a second satellite, wherein the second satellite is one of a plurality of satellites in a second satellite constellation. The method comprises the steps of evaluating a geometrical relationship between a second ground station and the satellites in the second satellite constellation, and directing communications between the second ground station and the second satellite according to the evaluated geometrical relationship.
Yet another aspect of the invention is embodied in a satellite constellation system comprising a means for performing the operations described above operations.
The invention achieves an overall optimization within technology limits, regulatory constraints, and market segment to provide broadband Internet Access for both residential and commercial users.
The invention also improves the spectrum sharing capability between geostationary orbit (GSO) and non-geostationary orbit (NGSO) satellite systems while providing protection to existing Ku-band satellite services. Areas considered that facilitate spectrum sharing include constellation architecture and spacecraft antenna, user terminal, payload architecture, and link budget design.
A constellation design is defined that provides non-uniform coverage correlated to the predicted market and globally distributed population while minimizing system investment (including the use of fewer satellites) while assuring that interference with existing GSO assets are minimized.
A link budget design is optimized under the constraints of supporting small-to-medium sized user terminals and medium rate data communications. The disclosed user terminals are less than one meter and the data rate is between 512 Kbps and 10 MBPS.
The invention applies direct radiated array antennas to achieve side lobe attenuation control while meeting the maximum effective power flux density (EPFD) requirement proposed by GSO satellite operators to avoid harmful interference to GSO links.
Resource management provides maximum capacity with minimal resources. A dynamic resource management engine is located at the network control center (NOC) to monitor the payload power level, spacecraft traffic demand, regional spectrum availability, and network statistics. It not only provides 100% communication connection but also adjusts system resources (such as power and spectrum utilization) based on an optimized resource assignment. As a result, the interference to incumbent space assets is minimized by reducing excessive effective isotropic radiated power (EIRP), and the spectrum efficiency is maximized.
The invention provides a phased service deployment. The selection of the constellation allows launching as few as 4 satellites to provide near global service. The present invention also discloses the augmentation of the satellite systems by the addition of MEO satellites to provide complete global connection with increased capacity based on technology maturity and service demand.
The system architecture of the present invention provides seven-beam cluster frequency reuse, allowing users to be connected to various networks, including Internet, Intranet, and Extranet, through local gateway stations (GS). Each GS serves adjacent areas within the seven-beam cluster and routes the traffic to appropriate terrestrial networks or another GS for communicating with the other system users through double hops. This allows subscribers to be connected everywhere around the globe.